The present invention relates to broach systems and particularly to a new and improved broach cutter assembly having disposable carbide inserts.
Broach tools have been used for many years for the machining of metal, and for specific operations such as broaching slots, openings or channels of specialized cross-section which are typically formed in turbine wheel discs. The conventional broaching tool has been a unitary broach having a plurality of cutting teeth formed on a single solid stick-like member. Several shortcomings, however, have been associated with the use of such stick-like broaches. For example, the quality of the overall tool is only as good as the worst tooth, with the existence of an undersized tooth resulting in an overloading of the next tooth, as well as making it necessary, through wear or otherwise, to discard the entire tool even though there is still useful life left in many or all of the other teeth. Of course, the entire tool is also lost as the result of any tooth damage or cracking with respect to any one tooth or any one part of the tool. In addition, the type of material from which the tool is made is restricted. More particularly, while high speed steels have been used to form the stick-like broaches, tougher, more expensive materials such as carbides cannot be used because of the prohibitive costs associated with the initial manufacture of the tool, as well as the cost of replacements necessitated by the fact that damage to any one part of the tool requires that it be discarded.
Another type of broaching tool which has been used is one which includes a plurality of separate cutting inserts which are fixed to the tool body. Typically, the inserts are formed from a cemented carbide or other hard metal. The conventional design for tools of this type is generally of brazed construction, i.e. carbide blanks are permanently fastened to a steel holder with braze material and ground after brazing to the required cutter configuration. Proper brazing of the carbide to the steel along with grinding the carbide after brazing is critical, yet due to space limitations, is extremely difficult. The brazing of the carbide tips requires that each be held in proper position during the braze procedure to facilitate grinding to form after brazing. Furthermore, it is necessary for a successful broaching operation that each tip is securely and properly brazed to the steel body. Unfortunately, it is often common for a brazed joint to come apart in the grinding operation or in the actual broaching of the part. In either event, if the carbide tip breaks, a new tip must be rebrazed and the form reground. The conventional brazed construction thus offers little advantage over high speed tooling since downtime and requalifying of a broach set is a lengthy process. In addition to broaches having brazed inserts, there are tools in which the cutting inserts are in some way clamped to the tool. Examples of such tools are disclosed in U.S. Pat. No. 3,707,748 to Price et al, issued Jan. 2, 1973, and entitled "Cutting Tool For Holding A Plurality Of Disposable Cutting Inserts;" U.S. Pat. No. 3,548,474 to Meyer, issued Dec. 22, 1970, and entitled "Machine Tool;" U.S. Pat. No. 3,641,642 to Schmidt, issued Feb. 15, 1972, and entitled "Individual Tooth Broach;" U.S. Pat. No. 3,528,154 to Schmidt, issued Mar. 28, 1968, and entitled "Individual Tooth Broach;" and Russian Pat. No. 727357/25 to Komler, issued Apr. 19, 1961 and entitled "Assembled Broach For Complex Profiles."
It is an object of the present invention to provide a new and improved broach system having disposable carbide inserts which are mounted in a series within a slot in a holder and cammed into position by clamp means.
A more specific object of this invention is to provide a new and improved broach system for broaching dovetail slots in turbine wheel discs wherein disposable carbide inserts are positioned within a slot in a broach holder and clamped in place by means of side and front clamps which also precisely position the inserts against particularly configured surfaces of the holder.